This invention relates to the reception and synchronisation of digital signals, and particularly digital audio signals.
In large multichannel digital audio systems FIFO (first in, first out) stores are commonly used to delay audio samples for synchronisation purposes. Constraints are placed on the relative timing of the read and write operations for these stores. Such a store has a "busy" output line which is enabled whenever either a write operation or a read operation takes place which inhibits any simultaneous attempt at a read or write operation respectively.
In normal operation write and read operations take place alternately. However, if the write and read operations occur more or less in phase with one another, then a small amount of jitter or timing uncertainty on the received samples may have the effect of momentarily reversing the order in which the write and read operations occur. This will result either in repeated samples or in lost samples, and consequent degradation of the sound quality.
This is illustrated in FIG. 1 of the drawings, which shows WRITE and READ operations in four different situations. In case A, the READ and WRITE pulses are widely separated in time. In case B, READ and WRITE are closer than the maximum timing uncertainty, which is represented by the shaded regions. The result of this can be as in case C, where READ and WRITE occur in what is effectively a random order each cycle.
This is thus an example of a situation where an asynchronous input signal subject to sample-to-sample jitter is required to be synchronised with a local reference by the use of a read-write buffer memory.